Southampton manager Nigel Adkins says Tadanari Lee has begun training at the Championship club.
Lee, who currently plays for Sanfrecce Hiroshima in the J-League, flew into London on Tuesday to discuss a move to Championship leaders.
The 26-year-old will train with Saints until a work permit arrives.
"The opportunity has arisen for him to come in a train with us with a view to trying to sign him permanently," Adkins told BBC Radio Solent.
Born to Korean parents in Tokyo, Lee scored the winning goal against Australia as Japan lifted a record fourth Asian Cup last year.
He would be the first Japanese player to sign for Southampton.
"The work permit process is going to take time and have got to work through that but he has been training with us this week and has been made welcome," added Adkins.
"I actually highlighted him to the players last year after he scored an amazing winning goal in the Asian Cup final."